In the 3rd Generation Partnership Project (3GPP), a radio access method (Evolved Universal Terrestrial Radio Access, EUTRA) and a radio access network (Evolved Universal Terrestrial Radio Access Network, EUTRAN) for cellular mobile communications have been considered. EUTRA and EUTRAN are also referred to as Long Term Evolution (LTE). In LTE, a base station device is also referred to as an evolved NodeB (eNodeB), and a terminal device is also referred to as user equipment (UE). LTE is a cellular communication system in which an area is divided into multiple cells to form a cellular pattern, each of the cells being served by a base station device. A single base station device may manage multiple cells.
In 3GPP, proximity based services (ProSe) has been considered. ProSe includes ProSe discovery and ProSe communication. ProSe discovery is a process that identifies that a terminal device is in proximity of a different terminal device, using EUTRA. ProSe communication is communication between two terminal devices that are in proximity of each other, the communication being performed through an EUTRAN communication path established between the two terminal devices. For example, the communication path may be established directly between the terminal devices.
ProSe discovery and ProSe communication are also referred to as device to device (D2D) discovery and D2D communication, respectively. Furthermore, ProSe discovery and ProSe communication are collectively referred to as ProSe. Moreover, D2D discovery and D2D communication are collectively referred to as D2D. A communication path is also referred to as a link.
NPL 1 describes that a subset of resource blocks is reserved for D2D, a network configures a set of D2D resources, and terminal devices are allowed to transmit D2D signals with the configured resources.